1. Field of the Invention
The present invention relates to a non-aqueous electrolyte secondary battery for use in a power source for a portable electronic apparatus or the like, and more particularly to an improvement in the shape of a battery.
2. Related Background Art
Since new portable electronic apparatuses including camera-video tape recorder hybrid apparatuses, portable telephones and laptop computers have been widely used in recent years, a need for rechargeable secondary batteries has arisen in place of disposable primary batteries.
Hitherto, hydraulic electrolyte secondary batteries have been employed which include nickel-cadmium batteries. The foregoing hydraulic electrolyte secondary batteries, however, suffer from excessively low discharge potentials. What is worse, the weight and volume of the battery cannot satisfactorily be reduced. Thus, a requirement for raising the energy density cannot be met.
Therefore, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, have been suggested and put to practical use because of their higher energy densities than those of the hydraulic electrolyte secondary batteries.
The non-aqueous electrolyte secondary batteries have been formed into cylindrical batteries each having an electrode device wound into a spiral shape and inserted into a cylindrical battery can; laminated electrode devices formed by laminating folded electrodes or positive and negative electrodes in the form of rectangles; and rectangular batteries each of which is formed by inserting, into a rectangular battery can, a coil electrode device constituted by winding elongated positive and negative electrodes. The rectangular battery has a space efficiency superior to that of the cylindrical battery.
The size and weight of each portable electronic apparatus have furthermore been reduced. Also the thicknesses of the apparatuses have been reduced. It leads to a fact that reduction in the thickness of the second batteries serving as the power sources for the electronic apparatuses has been required.
The conventional rectangular and non-aqueous electrolyte secondary batteries have a structure as shown in FIG. 1 that an opening 21a is formed in a surface of a battery can 21 having a minimum area. Therefore, the battery can 21 required to have a reduced thickness cannot easily be machined in spite of a large quantity of active substances which can be accommodated in the battery can 21.
When further reduction in the thickness of the battery is required, also the thickness of an electrode device 22 which must be accommodated in the battery can 21 is reduced. As a result, the hardness of the electrode device 22 decreases in a direction indicated by an arrow X shown in FIG. 1. Therefore, there arises a problem when the electrode device 22 is inserted into the battery can 21 in a direction (indicated by an arrow Y shown in FIG. 1) in parallel with a direction in which the electrodes are stacked. That is, the electrode device 22 is undesirably deformed because of contact resistance caused between the electrode device 22 and the inner surface of the battery can 21, as shown in FIG. 2. As a result, the electrode device 22 cannot easily and smoothly be inserted into the battery can 21.
If the thin battery is employed, the terminal cannot easily be formed on a battery cover which is provided for the surface of the battery can having the minimum area. In this case, a space for a safety unit, such as a split valve, cannot easily be obtained. Moreover, a lead wire which must be drawn out from the terminal of the battery to an electronic apparatus cannot easily be welded.
To easily insert the electrode device into the battery can, it might be considered feasible to employ a method in which the thickness of the electrode device is reduced. Thus, the clearance between the battery can and the electrode device is enlarged in order to reduce the contact resistance. In the foregoing case, pressure which can be applied to the electrode device is, however, lowered. Thus, force for bringing the positive electrode and the negative electrode into hermetic contact with each other is reduced. As a result, movement and reactions of ions cannot smoothly be performed. Hence, there is apprehension that satisfactory characteristics cannot be obtained from the battery.
In view of the foregoing, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having a structure with which an electrode device can easily be inserted into a battery can thereof and a terminal can easily be formed even if the thickness of the battery is considerably reduced.
To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery comprising: a battery can which accommodates an electrode device and non-aqueous electrolyte, wherein a largest opening of the battery can is hermetically sealed by a battery cover incorporating a terminal.
It is preferable that the battery cover has a safety unit which outwards releases internal pressure of the battery when the internal pressure of the battery has been raised to a predetermined pressure.
It is preferable that the safety unit incorporates at least a member, which is selected from a group consisting of a current interrupting unit and a Positive Temperature Coefficient device, and a split valve.
It is preferable that the battery cover has an electrolyte injecting opening through which the electrolyte is injected.
It is preferable that the electrode device is formed into a laminate constituted by laminating a positive electrode and a negative electrode substantially in parallel with the battery cover through a separator.
It is preferable that leads drawn out from the electrode device and laid substantially in parallel with the battery cover are connected to the terminal.
It is preferable that the battery can is formed into a rectangular shape.
It is preferable that the height of the battery can from a bottom surface thereof to the battery cover is 0.5 mm to 6 mm.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.